javascript – Pressing enter in a form clicks a button, But I don’t want that to happen

I’m trying to create a search page, with different options for search engines.

The problem I’m having is that when I press enter inside the text input box, it presses the button that triggers the dropdown box

This is my form element

<form class="searchbox item" onsubmit="return null;">
            <button id="sedropbtn" type="button" onClick="dropdown(); return false;">
                <img id="selectedengine" src="">
                <i class="fa fa-caret-down"></i>
            <div id="sedropdownbox" style="visibility: hidden;">
                <button class="seoption" onclick="changesearchengine('ddg'); dropdown(); return false;"> <!-- DuckDuckGo -->
                    <img src=""><a>DuckDuckGo</a>
                <button class="seoption" onclick="changesearchengine('google'); dropdown(); return false;"> <!-- DuckDuckGo -->
                    <img src="./assets/engineicons/google.png"><a>Google</a>
                <button class="seoption" onclick="changesearchengine('bing'); dropdown(); return false;"> <!-- DuckDuckGo -->
                    <img src="./assets/engineicons/bing.png"><a>Bing</a>
                <button class="seoption" onclick="changesearchengine('yahoo'); dropdown(); return false;"> <!-- DuckDuckGo -->
                    <img src="./assets/engineicons/yahoo.png"><a>Yahoo</a>
            <input id="inputbox" type="text" placeholder="Search with DuckDuckGo">
            <div class="searchicon"><svg aria-hidden="true" focusable="false" data-prefix="far" data-icon="search" role="img" xmlns="" viewBox="0 0 512 512"><path fill="currentColor" d="M508.5 468.9L387.1 347.5c-2.3-2.3-5.3-3.5-8.5-3.5h-13.2c31.5-36.5 50.6-84 50.6-136C416 93.1 322.9 0 208 0S0 93.1 0 208s93.1 208 208 208c52 0 99.5-19.1 136-50.6v13.2c0 3.2 1.3 6.2 3.5 8.5l121.4 121.4c4.7 4.7 12.3 4.7 17 0l22.6-22.6c4.7-4.7 4.7-12.3 0-17zM208 368c-88.4 0-160-71.6-160-160S119.6 48 208 48s160 71.6 160 160-71.6 160-160 160z" class=""></path></svg>