问菜单项之间不需要的透明空格(边框不起作用)

EN

<nav>
    <ul class="nav"> <!-- Menu from https://css-tricks.com/targetting-menu-elements-submenus-navigation-bar/ -->
        <li><a href="http://www.neoadvent.tech/">Home</a></li>
        <li><a href="../services/index.html">Services</a>
            <ul class="align-left">
                <li><a href="../services/drug-formulation-services.html">Drug Formulation</a></li>
                <li><a href="../services/analytical-and-bioanalytical-services.html">Analytical & Bioanalytical Services</a></li>
                <li><a href="../services/thermal-analysis-by-tga-and-dsc-services.html">Thermal Analysis</a></li>
                <li><a href="../services/custom-synthesis-services.html">Custom Synthesis</a></li>
                <li><a href="../services/pharmacology-and-toxicology-services.html">Pharmacology & Toxicology</a></li>
                <li><a href="../services/regulatory-support-for-fda-filings-for–drugs-and–medical devices-services.html">Regulatory Support for Drugs & Medical Devices</a></li>
                <li><a href="../services/materials-testing-services.html">Materials Testing</a></li>
                <li><a href="../pdfs/catalog_of_chemical_reagents_and_materials.pdf">Catalog of Chemical Reagents & Materials</a></li>
                <li><a href="../services/food-analysis-for-safety-services.html">Food Analysis</a></li>
            </ul>
        </li>
        <li><a href="#">Technologies</a>
            <ul class="align-left">
                <li><a href="../technologies/api-micronization.html">API Micronization</a></li>
                <li><a href="#">Drug Delivery</a>
                    <ul class="align-left">
                        <li><a href="../technologies/drug-delivery/sol-gel-encapsulation.html">Sol-gel Encapsulation</a></li>
                        <li><a href="../technologies/drug-delivery/smart-hydrogels-and-biomaterials.html">Smart Hydrogels and Biomaterials</a></li>
                        <li><a href="../technologies/drug-delivery/electrorheologically-controlled-drug-release.html">Electrorheologically-Controlled Drug Release</a></li>
                        <li><a href="../technologies/drug-delivery/polyphosphazenes.html">Polyphosphazenes</a></li>
                    </ul>
                <li><a href="#">Materials Science</a>
                    <ul class="align-left">
                    <li><a href="../technologies/materials-science/coatings.html">Coatings</a></li>
                    <li><a href="../technologies/materials-science/structural-materials.html">Structural Materials</a></li>
                    <li><a href="../technologies/materials-science/viscosity-control-in-non-aqueous-systems.html">Viscosity Control: Non-aqueous Systems</a></li>
                    </ul>
                </li>
            </ul>
        </li>
        <li><a href="../services/api-storage.html">Bio-Pharma Storage</a></li>
        <li><a href="../about-us/index.html">About Us</a></li>
        <li><a href="../news/index.html">News</a></li>
        <li><a href="../about-us/contact.html">Contact</a></li>
    </ul>
</nav>

nav {
    display: block;
    width:100%;
    text-align: center;
}
nav ul {
    margin: 0;
    padding: 0;
    list-style: none;
}
.nav a {
    display: block;
    background-color: #003399;
    color: white;
    text-decoration: none;
    padding: .5em 1.4em .7em;
    font-size: 75%;
    letter-spacing: 1px;
    position: relative;
}
.nav {
    vertical-align: top;
    display: inline-block;
    border-radius: 6px;
}
.nav li { position: relative; }
.nav > li {
    float: left;
    border-bottom: 4px #aaa solid;
    margin-right: 1px;
}
.nav > li > a {
    margin-bottom: 1px;
}
.nav > li:hover, .nav > li:hover >a { border-bottom-color: #99ddff; }
.nav li:hover > a { color: #99ddff; }
.nav > li:first-child { border-radius: 4px 0 0 4px; }
.nav > li:first-child>a { border-radius: 4px 0 0 0; }
.nav > li:last-child {
    border-radius: 0 0 4px 0;
    margin-right: 0;
}
.nav > li:last-child >a { border-radius: 0 4px 0 0; }
.nav li li a { margin-top: 1px }
.nav li a:first-child:nth-last-child(2):before {
    content: "";
    position: absolute;
    height: 0;
    width: 0;
    border: 5px solid transparent;
    top: 50%;
    right: 5px;
}

/* submenu positioning*/
.nav ul {
    position: absolute;
    white-space: nowrap;
    border-bottom: 5px solid #99ddff;
    z-index: 1;
    left: -99999em;
}
.nav > li:hover > ul {
    left: auto;
    padding-top: 5px;
    min-width: 100%;
}
.nav > li li ul { border-left: 1px solid #fff; }
.nav > li li:hover > ul {
    /* margin-left: 1px */
    left: 100%;
    top: -1px;
}

/* arrow hover styling */
.nav > li > a:first-child:nth-last-child(2):before { border-top-color: white; }
.nav > li:hover > a:first-child:nth-last-child(2):before {
    border: 5px solid transparent;
    border-bottom-color: orange;
    margin-top: -5px
}
.nav li li > a:first-child:nth-last-child(2):before {
    border-left-color: #aaa;
    margin-top: -5px
}
.nav li li:hover > a:first-child:nth-last-child(2):before {
    border: 5px solid transparent;
    border-right-color: orange;
    right: 10px;
}
.align-left { text-align: left; }