For Newer version of Edwiser RemUI theme (It will work for version Edwiser RemUI 3.7.5 and above)

Apply this Code in Edwiser RemUI General setting > Custom CSS section

#nav-drawer{
display: none;
}
body {
margin-left: 0 !important;
}


Note: This will make navigation to certain pages difficult due to lack of Left Navigation. So we would suggest you add these links to the Header menu bar. Refer to the instructions given below for adding links to the Header menu:
Click Home > Site administration > Appearance > Theme settings
Scroll down to the Custom menu items field.
Moodle community|https://moodle.org
Scroll to the bottom of the page and click Save changes
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For Older version of Edwiser RemUI theme (It will work for versions till Edwiser RemUI 3.5.10, Edwiser RemUI 3.6.7 and Edwiser RemUI 3.7.4)

Apply this Code in Edwiser RemUI General setting > Custom CSS section

.site-menubar {
display:none;
}

.site-menubar-fold .page,
.site-menubar-unfold .page,
.site-footer {
margin-left: 0 !important;
}


Note: This will make navigation to certain pages difficult due to lack of Left Navigation. So we would suggest you add these links to the Header menu bar. Refer to the instructions given below for adding links to the Header menu:
Click Home > Site administration > Appearance > Theme settings
Scroll down to the Custom menu items field.
Moodle community|https://moodle.org
Scroll to the bottom of the page and click Save changes